1. Field of the Invention
This invention generally relates to tape recording/reproduction systems of the type having the capability of automatically finding a feature recorded on the magnetic type by detecting the inter-feature pauses between the recorded features, and thereupon of precisely positioning the selected feature relative to the tape head for replay.
More particularly, this invention relates to an improved apparatus for, and method of, reliably detecting, in a noise-free manner, inter-feature pauses between features in order to accurately control the selective replay of the recorded features.
2. Description of the Prior Art
Many features or programs are recorded on a recording medium such as a magnetic recording tape. Automatic feature finder systems have been proposed to replay on tape recording/reproduction systems features which have been pre-selected by the listener, while bypassing other features.
These automatic feature finder systems operate by detecting the inter-feature pauses, i.e. the blank areas between successive features on the tape on which no signals were recorded, while the tape is advancing at fast forward or rewind speed. The detected inter-feature pauses are then used to precisely position the selected feature at its beginning at the playback head, and to concomitantly change the tape speed to the playback speed. The number of inter-feature pauses is used to select from a plurality of recorded features just what features are to be selectively played, and in what order the selected features are to be played.
However, the automatic feature finder system may malfunction when noise signals are located within an intra-feature pause. At certain tape speeds, the voltage amplitude levels of the noise signals can exceed a predetermined voltage level which is used to indicate the presence of a feature. Hence, in some cases, the noise signals within a pause can cause the system to mistake the pause for a feature itself.
To explain in more detail, the playback head senses the tape and detects features and pauses thereon. The playback head generates electrical audio signals whenever it detects a feature. When the head detects a pause, no audio signals are generated. Low frequency noise signals are superimposed over the audio signal and within the pause. All of these signals are typically successively amplified, filtered, saturated, detected, noise-suppressed and conducted to a schmitt trigger circuit to generate a pulsed information signal, as described in detail in the co-pending U.S. application Ser. No. 133,731, filed Mar. 25, 1980, entitled "Apparatus for and Method of Distinguishing Pauses To Control Selective Replay in Tape Recording/Reproduction Systems," by Yamamoto, Nakahara and Kasai, the entire contents of which are hereby incorporated by reference.
In operation, the schmitt trigger circuit generates an output pulse whenever the input audio signal exceeds a predetermined threshold voltage value, thereby indicating the presence of a feature. Whenever the input signal is lower than the threshold value, then this condition represents the presence of a pause. If any noise signal is present within the pause, then the voltage levels of the noise signals must be lower than the threshold value, or else the schmitt trigger circuit will be triggered to falsely indicate that a feature, rather than a pause, is present.
Certain low-frequency noise signal levels within a pause are above the threshold value of the schmitt trigger circuit when the tape is in the play mode. At the fast forward or rewind modes, there are middle- and high-frequency noise signals which have amplitude levels above the aforementioned threshold value. At these faster speeds, the magnetic flux on the tape changes more rapidly with time and, in turn, the voltage levels of the audio and noise signals, as detected by the playback head, increase. The increased voltage levels for the various frequency noise signals in the playback or fast forward or rewind mode therefore lead to the false indication of a feature when, in fact, a pause is present on the tape. If even one inter-feature pause is missed by the detection circuitry, then the entire system will not selectively replay the features as desired by the listener.